a. Field of Invention
The invention relates generally to vibration damping, and, more particularly to damping of an automotive steering system by magnetorheological fluids.
b. Description of Related Art
A need exists for a system for damping steering wheel vibrations to levels less objectionable or undetectable to a driver; a system that may be easily and economically manufactured, and a system that operates efficiently and reliably under a variety of vibration conditions.
Steering wheel nibble is defined as an unexpected rotational vibration that the driver feels through the steering wheel. Steering wheel nibble, hereinafter referred to as steering wheel vibration, leads to a significant number of customer complaints on many vehicles, and may cause premature deterioration of vehicular components. Steering wheel vibration is generally caused by factors such as brake roughness, brake torque variation, tire/wheel imbalance, and road load input being transmitted through the steering system to the driver. Steering wheel vibration caused by brake torque variation, which is typically generated from disc thickness variation is usually referred to as xe2x80x9cbrake roughness.xe2x80x9d The rotational vibration on the steering wheel caused by unbalanced tires/wheels and road load is traditionally known as xe2x80x9cnibble.xe2x80x9d The vibration excitations from these three categories are all transmitted through the suspension system to the steering system, as shown for example in FIG. 1. Since steering wheel vibration is caused by many different vibration excitations, it is difficult to target each source of vibration with a general, yet effective engineering solution.
Because suspension plays a critical role in transmitting vibration from, for example, brake roughness, road load input and tire/wheel imbalance, hydraulic and/or elastomeric bushings have been conventionally used as the primary damper to reduce suspension vibration caused by such factors. One limit to this approach is the large package space required for components such as hydraulic bushings, which is often unavailable. The use of elastomeric bushings is also limited to vibration reduction for specific frequencies. Accordingly, major structural and chassis system redesigns are necessary to implement these solutions over a wide range of vibration frequencies. Moreover, the durability of these components is of major concern, and the cost of hydraulic bushings is very high.
Various conventional steering wheel vibration suppression methods and devices are known and disclosed, for example, in U.S. Pat. No. 6,296,280 to Struble et al., U.S. Pat. No. 6,279,952 to Van Wynsberghe et al., U.S. Pat. No. 6,120,046 to Daly, U.S. Pat. No. 6,152,488 to Hedderly et al., U.S. Pat. No. 5,794,508 to Gerigk, U.S. Pat. No. 5,549,837 to Ginder et al., U.S. Pat. No. 4,942,947 to Shtarkman, U.S. Pat. No. 4,503,952 to Hesse, U.S. Pat. No. 4,458,915 to Emery, and U.S. Pat. No. 3,941,401 to Allison.
The above-identified U.S. Patents generally employ methods such as hydraulic dampeners, viscosity control of rheological fluids, rubber sleeves, shock absorbers and magnetorheological (MR) fluids for steering wheel vibration suppression.
U.S. Pat. No. 5,549,837 to Ginder et al., describes MR fluids for vibration damping. The device of Ginder ""837 utilizes the shear force between a rotational moving part and MR fluids to provide braking force when a field is applied. However, Ginder ""837 is limited in application to purely axial, as opposed to rotary and axial, damping of a piston in a housing (see FIG. 3 of Ginder ""837). Moreover, the tie rod force caused by brake vibration in a vehicle is usually about 250 350 lbs. With such strong vibration forces, the pure shear force produced by the rotary MR device in Ginder ""837 is not sufficient to dampen this vibration unless the MR device is extremely large, which would render such a solution impractical.
For the U.S. Patents cited above, from a design and manufacturing standpoint, the manufacture of the relatively complicated vibration suppression devices of the past has resulted in a significant increase in the overall manufacturing cost of vehicles, which are typically manufactured by the hundreds of thousands. From an assembly standpoint, the assembly and installation of complex vibration suppression devices can be time-consuming and burdensome, and can also add significantly to the overall cost of a vehicle. Lastly, from a maintenance and use standpoint, conventional vibration suppression devices have frequently failed to suppress steering wheel vibrations over a wide range of vibration frequencies, and have often failed to provide a level of durability expected in today""s demanding consumer market.
The invention solves the problems and overcomes the drawbacks and disadvantages of the prior art steering wheel vibration suppression devices by providing a magnetorheological (MR)damping device that can be applied to a vehicle""s steering system to resist strong vibration forces caused by factors such as brake torque variation, wheel/tire imbalance, and road load input.
Thus, an aspect of the present invention is to provide a vibration damping device capable of effectuating low frequency vibration damping, and having a high damping force capability.
Another aspect of the present invention is to provide a device capable of simultaneous rotational and axial damping.
Yet another aspect of the present invention is to provide a device that may be packaged in a small space, without requiring significant vehicle structural redesign.
The invention accomplishes these aspects by providing a magnetorheological vibration damper for damping axial and rotational vibrations of an automotive steering system. The damper may include a housing encasing magnetorheological fluid therein and a rotor and orifice plate disposed within the housing. The rotor and orifice plate may include protrusions formed as teeth on its surface, and holes and/or slots. The rotor and orifice plate may be affixed to the automotive steering system or formed with the automotive steering system. Electric coils may also be provided within the housing for generating an electric field for activating the magnetorheological fluid.
For the damper described above, the cross-section of the housing and/or the rotor and orifice plate may be circular or elliptical. The teeth may extend fully or partially along an axial length of the rotor and orifice plate. The rotor and orifice plate may be formed with the automotive steering system or mounted to the automotive steering system. The holes and/or slots may extend fully or partially through the rotor and orifice plate along an axial length thereof, and may be disposed parallel or transverse to the central axis of the rotor and orifice plate. The damper may be mounted along a length of a steering shaft of a vehicle.
The present invention further provides a system for damping vibrations in a vehicle. The system may include the magnetorheological vibration damper, as described above. The system may further include a control system for controlling operation of the damper. The control system may include a steering wheel vibration sensor and a controller for activating the damper if a signal value from the steering wheel vibration sensor exceeds a predetermined threshold and deactivating the damper if the signal value is below the predetermined threshold. The controller may be programmable by a user to increase or decrease the predetermined threshold.
The present invention yet further provides a method of damping automotive steering system vibrations. The method includes the step of mounting a magnetorheological vibration damper to the automotive steering system. The method further includes the steps of flowing magnetorheological fluid through holes and/or slots in a rotor and orifice plate disposed within the damper, and flowing the magnetorheological fluid by protrusions on a surface of the rotor and orifice plate. The method yet further includes the step of activating the magnetorheological fluid by generating an electric field so as to cause axial and rotational damping of the automotive steering system.
Additional features, advantages, and embodiments of the invention may be set forth or apparent from consideration of the following detailed description, drawings, and claims. Moreover, it is to be understood that both the foregoing summary of the invention and the following detailed description are exemplary and intended to provide further explanation without limiting the scope of the invention as claimed.